DLR's Railway Collision Avoidance System (RCAS) is a 'safety overlay' system which can be deployed on top of any existing safety infrastructure in train networks. The core idea of RCAS is to broadcast the position and intended track of trains as well as additional data like vehicle dimensions to all other trains in the area using ad-hoc train-to-train communications. This enables train drivers to have an up-to-date accurate knowledge of the traffic situation in the vicinity, and act in consequence. Computer analysis of the received information, the own position and movement vector and an electronic track map detects possible collisions, displaying an alert signal, and advising the driver of the most convenient strategy to follow in order to avoid the danger. The system is adaptive to a variety of situations like advancing trains or road vehicles or obstacles.